When planning an engine build, one term that often pops up when discussing the bottom half of the short-block is “windage.” Now, this term shouldn’t be confused with the term “Kentucky windage,” which is something else altogether. If we use the Oxford definition, it states that windage is, “the air resistance of a moving object, such as a vessel or a rotating machine part, or the force of the wind on a stationary object.” If we drill down to automotive engines specifically, windage is defined by Canton Racing Products as, “the flow of air within the crankcase.”
Generally, when we say windage in the engine, we are referring to the effect windage has on the oil in the crankcase. All that air movement generated by motion within the crankcase can have a negative effect on the oil in the system in a number of ways. Then there is the physical effect that uncontrolled oil in your crankcase can have on the rotating assembly — drag. So let’s get to know what we are fighting, and then we’ll talk about how to effectively fight it.
Know Your Enemy — Windage’s Effects on your Engine
There are a number of avenues in which windage makes life in the crankcase less than ideal. When any liquid is churned with air, you get aeration. In the case of engine oil, aerated oil has a number of drawbacks. First, aerated oil doesn’t pump as smoothly. Excessive oil aeration can cause oil feed issues since oil pumps are designed to move fluid, not froth. Why oil-starvation issues are bad is pretty self-explanatory.
The second drawback of aerated oil is that engine oil mixed with air doesn’t dissipate heat at the same rate as clear liquid oil. Increased oil temperatures in the system lowers the actual viscosity of your oil, which reduces the oil’s ability to properly do its job within the engine. Combine elevated oil temperatures with frothing issues, and you can start to see a loss in oil pressure.
The next method through which windage can reduce your engine’s performance is through brute force. Ideally, the crankshaft would spin through clear air and only face air resistance. However, with oil splashing all around the crankcase, impacting the spinning counterweights and journal throws, that oil can cause a real and measurable amount of drag on the crankshaft.
Obviously, we try to reduce drag on the crankshaft in a multitude of ways when building an engine, so it only stands to reason that you address this source of potential power loss as well. Additionally, when the fast-moving crankshaft smacks into that oil, you (again) run the risk of oil aeration.
The third form of chaos that excessive windage can cause is another path to increased oil temperatures. By splashing that oil all over the cylinders and rotating assembly, it acts as a heat sink, pulling extra heat out of the components and cylinder walls and then introducing it into your oil supply.
While this can be an advantage when built into the system through piston cooling jets, in those systems, the extra heat is accounted for in the overall design of the system. (We won’t even touch the debate between the benefits of cooling the pistons vs. the drag induced by the weight of the oil sprayed onto the piston in this article.)
Fighting The Good Fight
Since we know the problems windage can cause and the methods through which it causes them, companies like Canton can effectively combat and mitigate the issue. “Mitigating windage is pretty pivotal in the design of our oil pans,” says Iann Criscuolo, Sales and Marketing Manager for Canton. “We have several features in our pans aimed solely at reducing windage.”
The engineers at Canton have four main methods through which windage is reduced or its effects mitigated. Remember, you can’t stop the movement of air that results from the crankshaft spinning through the crankcase, but you can control the oil.
First, is what is known as a crank scraper. While it doesn’t actually physically scrape the crankshaft like a razor blade against the skin, it does get quite close to the crank, physically, and traps oil coming off of the spinning crankshaft, preventing it from being slung upward into the crankcase.
Crank scrapers are probably the simplest form of windage control, and can even be implemented on stock oil pans in some cases. “We use crank scrapers in pans that either don’t have the clearance for, or don’t come standard with a windage tray,” says Criscuolo. “It captures droplets, breaks windage, and forces oil back to the pickup of the pan.”
Next is a feature Canton calls the “power pouch.” It operates on a principle similar to a crank scraper, but with much more engineering involved. It’s effectively a lateral “kick-out” in the oil pan, on the side of the pan in the direction of crankshaft rotation, which gives displaced, agitated oil a place to go after it has been scraped/slung off of the crankshaft.
“The pouch keeps the oil away from the rotating assembly, preventing it from getting whipped up and creating the heavy atmosphere in the crankcase,” explains Criscuolo. “Keeping oil away from the crankshaft is an effective method, and if you can’t make the pan deeper [because of application/chassis restraints], you can make it wider.” Rather than bouncing off the side of the pan, the baffled compartment adds volume to slow and trap the oil to prevent aeration and feed it back into the oil supply in a much more controlled manner.
Then, there is the aptly named windage tray. These come in a number of designs and are even included on some factory engines. The idea behind a windage tray is that they provide a physical barrier between the violently moving crank with the oil it’s throwing everywhere, and the oil supply, while still allowing oil to move back into the oil supply in a smoother, calmer manner.
There are several ways to accomplish this, but the two main designs utilize a louvered tray and a mesh tray. “I personally prefer the louvered designs, because it’s a solid piece of metal between the crankshaft and sump to break up any splash,” says Criscuolo. “That extra surface area breaking anything up is a good thing. However, the mesh is a one-way mesh design, so it does make it more difficult for droplets to make it back through. But that solid louvered design can also break up air motion inside the crankcase.”
Finally, there is a windage cover for the anti-slosh baffles in the sump itself. The trap door baffles inside of Canton’s oil pans are designed to control oil slosh under fore, aft, and lateral G-forces when driving, but by incorporating a top plate, which has an opening just large enough for the oil pump pickup, it further controls the oil by preventing the turbulent air from grabbing oil out of the sump. “The plate is meant to keep the oil down in the sump and not let it get whipped back up,” Criscuolo says.
Other Windage-Fighting Strategies
There are other ways in which windage is combated besides oil pan design. One of the more simple ones is simply through oil level. It’s long been a racer’s trick to run less than the normal amount of oil to reduce windage. While the proper oil level is a whole subject in and of itself, the idea behind running less oil is that with less volume there is less oil to slosh around, and the lower oil level is physically further from the spinning crankshaft.
Unfortunately, the risk of running less oil in your engine outweigh the reward in 99.9-percent of the cases. Besides running the risk of oil starvation under high G-forces, the reduced volume also has reduced heat capacity, which means elevated oil temperatures and the associated issues hot oil can cause. Those who run less oil than recommended in order to reduce windage are usually in competition settings, where an engine only runs for short periods, and the gains in power are worth the reduction in lifespan.
Another way that windage and its effect on the rotating assembly can be mitigated is through a process known as “knife-edging” the crank. That is where the leading edge of the counterweights are profiled to “slice” through any oil in its path, rather than smash through with a flat face. Callies even goes a step further with its “Ultra-Shed” counterweight profiling. That process profiles both the leading and trailing edge of the counterweight to move oil away from the counterweight, as well as direct oil away from the approaching rod journal as well.
As you can see after reading this article, windage is a common occurrence in any internal combustion engine, but its effects are intensified as engine speeds increase. This is both because velocity is an exponential component in the kinetic energy calculation, as well as the fact that with higher rotational speeds, events happen within a shorter period of time, allowing the oil less time to settle between the next event that disturbs it again.
While you might not need to go to the extremes of performance to mitigate windage, taking some steps to fight the effects of windage in your performance project will lead to tangible benefits in the long run.